The present invention relates to patch antennas and more particularly to an improved patch antenna with increased bandwidth.
As understood that an antenna is used in transmitting electromagnetic waves (i.e., signals) generated by an electronic device to the air or receiving signals by the electronic device. Hence, antennas have been widely provided in various electronic devices as ubiquitous elements. As such, a quality of transmitted or received signal strongly depends on performance of an antenna provided in the electronic device or whether an antenna characteristic is matched with the electronic device. Further, a high performance radio frequency (RF) circuit and digital circuit of an electronic device can be carried out only by incorporating a high quality antenna. In this regard, all electronic product designers and manufacturers pay a great attention to quality of antenna in the manufacturing process or even performance test of antenna in the finished electronic product.
Conventionally, antennas are classified based on their structures and characteristics as detailed below.
(1) Patch antenna: Referring to FIG. 1, a patch antenna 10 comprises a substrate 11 made of ceramic material. In detail, the substrate 11 is formed by heating a ceramic material, molding the melted ceramic material to produce a ceramic plate, and finally sintering the ceramic plate. A patch 12 and a ground plane 13 both of rectangle or square are printed on top and bottom surfaces of the substrate 11 by photolithography and etching respectively. Further, a feed pin 14 is pierced through the patch 12 and the ground plane 13 to connect to a signal wave feed line (e.g., coaxial cable) 15. As a result, a resonant cavity is formed between the patch 12 and the ground plane 13. A high frequency electromagnetic field is generated in the resonant cavity. The electromagnetic field is then radiated from a gap between the patch 12 and the ground plane 13. The patch antenna 10 is advantageous due to compactness, enhanced structural strength, high dielectric coefficient and low temperature coefficient of ceramic, good heat-resistant characteristic, low power loss, and applicable to various environments. A typical implementation of the patch antenna 10 is a ceramic patch antenna provided in a GSM (Global System for Mobile) based cellular phone. However, the patch antenna 10 also has a number of disadvantages. For example, a manufacturing process of the patch antenna 10 is complicated, resulting in a high manufacturing cost. Further, the signal wave feed line 15 such as coaxial cable has several drawbacks, e.g., time consuming in installation, the requisite provision of the additional feed pin 14, a welding of the feed pin 14 to the patch 12 and the substrate 11, and poor antenna quality caused by failed welding.
(2) Patch antenna having a patch line as feed line: Referring to FIG. 2, a patch antenna 20 comprises a substrate 21 formed on a circuit board. A patch 22 and a ground plane 23 both of rectangle or square are printed on top and bottom surfaces of the substrate 21 by photolithography and etching respectively. A patch line 24 is extended from a center of a side of the patch 22 to an edge of the substrate 21 so as to serve as a signal wave feed line. A gap 221 is formed at either side of the patch line 24 to separate the patch line 24 from the patch 22. As seen that a substantially W-shaped (i.e., circuitous) current path W indicated by dash line is formed along edges of the patch 22 and patch line 24 adjacent the gaps 221. Such arrangement can increase the current path W, resulting in a size reduction of the patch antenna 20. However, a very large inductance is generated by the circuitous current path W caused by forming the gaps 221 and the current path W passing two projections 222 each adjacent the gap 221. The strong inductance will adversely affect gain and bandwidth of the patch antenna 20, resulting in a prohibition of bandwidth increase.
(3) Patch antenna having a coplanar wave-guide as feed line: Referring to FIG. 3, a patch antenna 30 comprises a substrate 31 formed on a circuit board. A patch 32 and a ground plane 33 both of rectangle or square are printed on top and bottom surfaces of the substrate 31 by photolithography and etching respectively. A space 331 is formed in the ground plane 33. A patch line 34 is printed in the space 331. A signal wave feed line is coupled to the patch 32 from one end of the patch line 34 by means of a coplanar wave-guide. However, such antenna is undesirable due to complicated structure, design difficulty, tedious manufacturing process, and high cost.
Moreover, typically for increasing a bandwidth of patch antenna construction of the antenna is changed by patch antenna designers and manufacturers. As such, at least two resonant patterns are produced, resulting in an increased bandwidth in adjacent frequency bands. However, such is difficult to design. Further, thus produced antenna may be bulky due to practical considerations, thereby contradicting the trend of compactness. Hence, a need for improvement exists.
A primary object of the present invention is to provide a patch antenna with increased bandwidth. By utilizing this, the above drawbacks as experienced by patch antenna designers and manufacturers in attempting to increase the bandwidth of patch antenna can be overcome.
One object of the present invention is to provide a patch antenna including a patch and a ground plane printed on top and bottom surfaces of a dielectric substrate respectively by a technique the same as manufacturing a printed circuit board. The patch has a size smaller than that of the dielectric substrate. The antenna further comprises a patch line extended from a center of a side of the patch to an edge of the dielectric substrate for serving as a signal wave feed line of the patch antenna, and a gap provided at one side of the patch line to separate the patch line from the patch for forming a circuitous current path from one edge of the patch line along the sides adjacent the gap to one side of the patch. By the provision of the gap, the patch antenna can significantly reduce inductance generated by signal wave, increase an effective bandwidth, and significantly reduce design and manufacturing costs by means of a simple structure being easy to manufacture.
In one aspect of the present invention, the size and the shape of the gap between the one side of the patch line and the patch can be modified so as to obtain an improved signal matching.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.